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Airplane on a Conveyor Belt

How can an airplane take off if it is on top of a conveyor belt moving in the opposite direction?

The first question to ask is, “How does an airplane move itself forward?” An airplane moves itself forward using its propellers or jets, not its wheels. And unlike wheels, these mechanisms aren’t really concerned with what is happening on the ground. A grassy field, a runway, a conveyor belt, a lake of molten lava—no matter the terrain, the propellers or jets would still push the plane forward. But taking off is another matter...it can be pretty difficult if lava has melted off the bottom half of the plane.

So we know what moves a plane forward, but how does it lift off? As the the plane is propelled forward, its wings pass through the air. This creates lift, or the upward force that pushes an airplane into the air. As long as wind is moving past the wings, lift will be generated. If enough lift is generated, the plane will lift off the ground.

In fact, the lift alone can actually cause an airplane to take off without the help of propellors or jets. Imagine a small airplane sitting on the ground as a huge windstorm hits. If enough air is blown past the wings, it will generate lift and then up, up and away.

 

The Science of Lift

There are two ways lift can be generated by airplane wings.

  1. Angle of Attack – Wings on airplanes do not sit flat, they are angled to push air down as it passes the wings. These wings force air above them downwards. This decreases the air pressure above the wings, transferring that pressure below the plane. This pressure provides enough lift to keep the plane in the air.
  2. Bernoulli Pressure – In 1738 Daniel Bernoulli discovered that when the speed of air increases, its pressure decreases. Why is this important? Well, the speed of air increases as it passes over the curved top of an airplane wing. As it does this, the air pressure above the wing decreases, allowing the pressure under the wing to increase. The higher air pressure under the wing pushes upwards, providing lift to the wing.

 

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